The present invention relates to golf balls and more particularly, the invention is directed to golf balls with increased resilience and high density center.
The spin rate of golf balls is the end result of many variables, one of which is the distribution of the density or specific gravity within the ball. Spin rate is an important characteristic of golf balls for both skilled and recreational golfers. High spin rate allows the more skilled players, such as PGA professionals and low handicapped players, to maximize control of the golf ball. A high spin rate golf ball is advantageous for an approach shot to the green. The ability to produce and control back spin to stop the ball on the green and side spin to draw or fade the ball substantially improves a player""s control over the ball. Hence, the more skilled players generally prefer a golf ball that exhibits high spin rate, in part, off scoring irons, such as the 7-iron club through the pitching wedge.
On the other hand, the recreational players who cannot intentionally control the spin of the ball generally do not prefer a high spin rate golf ball. For these players, slicing and hooking the ball are the more immediate obstacles. When a club head strikes a ball improperly, an unintentional side spin is often imparted to the ball, which sends the ball off its intended course. The side spin reduces a player""s control over the ball, as well as the direct-line distance the ball will travel. A golf ball that spins less tends not to drift off-line erratically if the ball is not hit squarely with the club face. A low spin ball will not cure the hook or slice, but will reduce the adverse effects of the side spin. Hence, recreational players typically prefer a golf ball that exhibits low spin rate.
Reallocating the density or specific gravity of the various layers of a golf ball provides an important means of controlling the spin rate. In some instances, the weight from the outer portions of the ball is redistributed toward the center to decrease the moment of inertia, thereby increasing the spin rate. For example, U.S. Pat. No. 4,625,964 discloses a golf ball with a reduced moment of inertia having a core with specific gravity of at least 1.50 and a diameter of less than 32 mm and an intermediate layer of lower specific gravity between the core and the cover. U.S. Pat. No. 5,104,126 discloses a ball with a dense inner core having a specific gravity of at least 1.25 encapsulated by a lower density syntactic foam composition. U.S. Pat. No. 5,048,838 discloses another golf ball with a dense inner core having a diameter in the range of 15-25 mm with a specific gravity of 1.2 to 4.0 and an outer layer with a specific gravity of 0.1 to 3.0 less than the specific gravity of the inner core. U.S. Pat. No. 5,482,285 discloses another golf ball with reduced moment of inertia by reducing the specific gravity of an outer core to 0.2 to 1.0.
In other instances, the weight from the inner portion of the ball is redistributed outward to increase the moment of inertia, thereby decreasing the spin rate. U.S. Pat. No. 6,120,393 discloses a golf ball with a hollow inner layer with one or more resilient outer layers, thereby giving the ball a soft core, and a hard cover. U.S. Pat. No. 6,142,887 discloses an increased moment of inertia golf ball comprising one or more layer layers made from metals, ceramic or composite materials, and a polymeric spherical substrate disposed inwardly from the layer layers.
These and other references disclose specific examples of high and low spin rate ball with ranges of specific gravity, ranges of diameter for the core and ranges of thickness for the outer layers, etc. They, however, do not offer a high spin rate golf ball with a high density inner core and a resilient outer core wherein both the spin rate and resilience are maximized by controlling both the specific gravity and diameter of the inner core and the composition and diameter of the outer core. Hence, there remains a need in the art for an improved golf ball with controlled spin rates.
The present invention is directed to a golf ball with an inner core of a predetermined specific gravity and diameter.
The present invention is further directed to a golf ball with multi-layer core, wherein the outer core layer contains substantially no filler, or in other words it contains filler in an amount that is less than or equal to five parts of filler to 100 parts of polymeric material.
In one embodiment, the present invention encompasses a golf ball comprising a core having an inner core and an outer core and which is encased by a cover having a thickness from about 0.010 inch to about 0.080 inch, wherein the inner core has a specific gravity of at least about 3 and a diameter of about 0.40 inch to about 0.60 inch.
In another embodiment, the present invention encompasses a golf ball wherein the specific gravity of the inner core is from about 3 to about 4 and comprises a polymeric matrix comprising polyurethane, polyurea, or a combination thereof. In one embodiment, the inner core polymeric matrix is substantially free of polybutadiene.
In yet another embodiment of the present invention, the inner core comprises high specific gravity filler incorporated in a polymeric matrix, preferably tungsten powder. Additionally, the high specific gravity filler may be selected from a group consisting of metal powder, metal alloy powder, metal oxide, metal stearates particulates and carbonaceous materials. Also, the high specific gravity filler may be selected from a group consisting of bismuth powder, boron powder, brass powder, bronze powder, cobalt powder, copper powder, inconel metal powder, iron metal powder, molybdenum powder, nickel powder, stainless steel powder, titanium metal powder, zirconium oxide powder, aluminum flakes, tungsten metal powder, beryllium metal powder, zinc metal powder, tin metal powder, zinc oxide, iron oxide, aluminum oxide, titanium dioxide, magnesium oxide, zirconium oxide and tungsten trioxide.
In another embodiment, the diameter of the inner core is from about 0.45 inch to about 0.55 inch, more preferably about 0.5 inch. Also, preferably the inner core comprises polyurethane.
In another embodiment, the outer core has a specific gravity of about 1.0 to about 1.1. The outer core preferably comprises a polymeric material substantially free of fillers. If present, the amount of fillers within the polymeric matrix of the outer core is less than about 3 phr to 100 phr of polymeric outer core material.
In one embodiment of the present invention, the golf ball""s outer core is made of a polymeric matrix selected from a group consisting of natural rubber, polybutadiene, polyisoprene, styrene-butadiene or styrene-propylene-diene rubber, ionomer resins, polyamides, polyesters, thermoplastic elastomer, polyether amide copolymers, polyether ester copolymers, thermoplastic urethane, styrenic block copolymers elastomers, metal salt of a fatty acid, partially or fully neutralized ionomer, metallocene or other catalyzed polymer, castable material, urethane, polyurea, epoxy, silicone, interpenetrating polymer networks, and a melt processible composition, which comprises a highly neutralized ethylene copolymer and one or more aliphatic, mono-functional organic acids having fewer than 36 carbon atoms of salts thereof, wherein greater than 90% of all the acid of the ethylene copolymer is neutralized. Optionally, the outer core further comprises at least one sulfur compound.
When the outer core comprises polybutadiene, preferably the butadiene has a Mooney viscosity from about 40 to about 80. More preferably, the butadiene has a Mooney viscosity is from about 40 to about 60. In yet another embodiment, the outer core has a specific gravity in the range of about 1.0 to about 1.1. Preferably, the outer core is made of polybutadiene and has a specific gravity of about 1.06.
In yet another embodiment, the golf ball has a cover, wherein the cover thickness is about 0.01 inch to 0.08 inch. The cover may be in the form of a sandwich cover and wherein the sandwich cover comprises an inner cover layer and outer cover layer comprising a first polymeric material and an intermediate cover layer comprising a second polymeric material. In an alternative embodiment, the cover comprises an inner cover layer and an outer cover layer. The inner cover may comprise an ionomer having a Shore D hardness of greater than about 60, preferably having Shore D hardness from about 60 to about 80, and more preferably, Shore D hardness from about 69 to about 74.
In an embodiment, the golf ball of the present invention has an outer cover comprising a urethane having a Shore D hardness of less than about 65. Preferably, the urethane has a Shore D hardness of about 30 to about 60. The cover may comprises a material selected from a group consisting of polyurethane, partially or fully neutralized ionomer, polyurea, polyurethane ionomer, metallocene or other catalyzed polymer, silicone, metal salt of a fatty acid and melt processible composition, which comprises a highly neutralized ethylene copolymer and one or more aliphatic, mono-functional organic acids having fewer than 36 carbon atoms of salts thereof, wherein greater than 90% of all the acid of the ethylene copolymer is neutralized.